Project Summary/Abstract The formation and maintenance of bilateral symmetry in animal development is poorly understood. This process is intimately related to many developmental abnormalities such as scoliosis and neural tube defects. The rudimental animal body shape forms during early embryo morphogenesis in parallel to the differentiation of distinct tissue types. The molecular players, cellular processes and physical forces driving the symmetric and straight growth of these tissues remain to be disentangled. Here I propose an interdisciplinary approach that combines imaging, theory, biomechanical measurement and perturbations to identify the mechanisms ensuring body axis symmetry in avian embryos. In the mentored K99 phase of this project, I will construct a 4- dimensional dataset of chicken embryos covering the stages of body axis formation. To do so, I will develop live imaging pipelines at both tissue and cellular resolution and will register quantitative measurements from the movies to a reference framework. This information will allow me to develop biophysical models that hypothesize how cellular dynamics produce tissue forces. I will also use these models to probe the constraints on the robustness of the symmetry outcome and to identify key parameters that control variability. In parallel I will perform serial surgical ablations on different body axis tissues and observe the impact on symmetry. Using molecular perturbations, I will test the roles of cell division, cell movement and cell signaling (fibroblast growth factor and retinoic acid) in tissue and cell response to asymmetry. To measure tissue forces that extend and straighten the body, I will implant soft gels and measure their deformation to assess the forces the neighboring tissues exert on the implant areas. I will also use magnetic tools to produce defined forces on tissues and record responses. To achieve quantitative results, I will test a range of high-sensitivity methods including cantilevers and pressure sensors. With these datasets and tools developed, in the R00 phase I will begin to produce spatial-temporal maps of force distribution. By aligning this map to tissue geometry, cell dynamics and molecular activity data, I will be able to make systematic comparison and create models that explain the generation of forces from molecular and cellular activities and how they ensure robust bilateral symmetry. I will also use these results to reveal principles of mechanical interactions between tissues that are an important and understudied aspect of normal and abnormal development. While I have extensive experience in molecular genetics, embryology, live imaging and modeling, the K99 award will allow me to receive training in mathematics, physics and engineering. My proposed training and research activities will benefit tremendously from the unique and complementary expertise of my mentors and collaborators. The project will take place in the strong, interdisciplinary research environment integrating Brigham Women?s Hospital and Harvard University. This project will greatly enhance my career development, promote our quantitative understanding of developmental defects, and provide guidance to tissue engineering and regenerative medicine.